The M8 generated some additional interest in rangefinder photography by making it a topical subject. For example, The New Yorker Leica profile was clearly motivated by the introduction of the M8. At the same time, the premium price of the M8 significantly limits the number of people who will sit down their DSLR and give the rangefinder world a try. Prior to owning my Epson R-D1, I was not a rangefinder photographer and would have never become one if the M8 was the only digital option.
For me, the real importance of the M8 lies not in its popularity but the historical statement it makes. Though I own an R-D1, I always felt Epson presented this camera as a limited issue historical oddity, like those replicas of 1940's radios that play CD's. By releasing the M8, Leica saved the rangefinder camera from becoming an antiquarian photographic method tossed on the historical pile with Daguerreotypes, glass negatives, and twin lens reflexes. If Voigtlander or another camera maker could produce a good digital rangefinder at a around $1500, the rangefinder world would probably be transformed by that camera.